20(S)-camptothecin (CPT) is a natural alkaloid product which is present as a component in a crude plant material isolated from the Chinese tree Camptotheca acuminata (Nyssaceae) (Wall, M.; Wani, M. C.; Cooke, C. E.; Palmer, K. H.; McPhail, A. T.; and Slim, G. A., "Plant antitumor agents. I. The isolation and structure of camptothecin, a novel alkaloidal leukemia and tumor inhibitor from Camptotheca acuminata", J. Am. Chem. Soc. 88:3888-3890, 1966). CPT can also be isolated from the Indian tree Mappie foetida Miers (Govindachari, T. R. and Viswanathan, N., "Alkaloids of Mappia Foetida", Phytochemistry 11:3529-3531 (1972)). CPT has been determined to possess considerable antitumor activity (Wani, M. C. and Wall, M. E. "Plant Antitumor Agents. II. The Structure of Two New Alkaloids from Camptotheca acuminata", J. Org. Chem. 34(5):1364-1367 (1968) and has since been the focus of much scientific endeavor (See reviews: 1) Shamma, M.; St. Georgiev, V.; Journal of Pharmaceutical Sciences 63(2):163-183 (1974); 2) D'Arpa, P. and Liu, L. F. "Topoisomerases-targeting antitumor drugs" Biochimica et Biophysica Acta. 989:163177 (1989); 3) Corcoran, J. W. and Hahn, F. E. "Mechanism of Action of Antimicrobial and Antitumor Agents" Antibiotics, Vol. III, Springer-Verlag, New York, Heidelberg, Berlin, pp. 48-57 (1975); 4) Hutchinson, C. R. "Camptothecin: Chemistry, Biogenesis and Medicinal Chemistry", Tetrahedron 37:1047-1065 (1981); 5) Cai, J. C. and Hutchinson, C. R., "Camptothecin", The Alkaloids, Vol. XXV, pp. 101-137 (1983)). Recently, it was shown that CPT has high activity against human cancer xenografts in vivo (Giovanella, B. C.; Hinz, H. R.; Kozielski, A. J., Stehlin, Jr., J. S.; Silber, R. "Complete Growth Inhibition of Human Cancer Xenografts in Nude Mice by Treatment with 20(S)-camptothecin", Cancer Research, 51:3052-3055 (1991)), as well as in vitro (Pantazis, P.; Hinz, H. R.; Mendoza, J. T.; Kozielski, A. J.; Williams, Jr., L. J.; Stehlin, Jr., J. S.; Giovanella, B. C. "Complete Inhibition of Growth Followed by Death of Human Malignant Melanoma Cells In Vitro and Regression of Human Melanoma Xenografts in Immunodeficient Mice by Camptothecins," Cancer Research, 52:3980-3987 (1992)). It is of interest that a highly efficient method be developed for the purification of CPT since CPT is generally commercially available only as a plant extract.
The traditional methods of purifying CPT involve the use of conventional chromatography using a mixture of solvents, usually a nonpolar solvent in conjunction with a polar solvent to affect the separation of individual molecules from each other with silica gel, followed by crystallization from methanol-acetonitrile. (Wall, M. E., Fourth International Symposium on the Biochemistry and Physiology of Alkaloids, Halle, DDR, Jun. 25-28, 1969, pp. 77-87; Wall et al. 1966, supra. )